The goal of this proposal is to introduce a novel gene therapy approach for reversing progressive autoimmune diseases, such as multiple sclerosis and rheumatoid arthritis. Initial studies will emphasize animal models in which disease producing epitopes have been identified. The rationale is based on the finding that adult mice injected i.v. with bone marrow or peripheral cells expressing bacteriophage lambda cI epitope 12-26 in frame with an IgG carrier become profoundly tolerant to this determinant at both the B and T cell levels. This state of unresponsiveness can be induced in previously immunized animals. Since the bone marrow-derived cells in the periphery continue to produce and present the tolerogenic epitopes to newly generated T cells, the experiments proposed herein will offer an opportunity to both induce and maintain tolerance to autoantigens by host antigen presentation. My hypothesis is that B cells are tolerogenic APC and that this protocol favors B cell presentation. Retroviral vectors, constructed to express myelin basic protein or collagen epitopes on an IgG scaffold, will be used to infect bone marrow and peripheral hematopoietic progenitor cells, which will then be injected into adult mice before and after induction of experimental allergic encephalomyelitis (EAE) or collagen induced arthritis. The aims of this project are: 1) To develop novel genetically-engineered constructs for the expression of myelin basic protein (MBP) and its immunodominant determinants as part of an IgG tolerogenic carrier. 2) To test the efficacy of these novel constructs to abrogate the immune response to MBP in susceptible strains in order to prevent and treat EAE. 3) To optimize this protocol for transfection into long-term bone marrow cultures containing B cell precursors for transfection with these constructs. 4) To test if our findings in the EAE model can be applied to another autoimmune models, e.g., collagen induced arthritis.